A grey fine-grained volcanic rock consisting largely of alkali feldspar.
- ‘Its occurrence is largely restricted to relatively unusual alkalic igneous rocks, such as sodic granites, certain syenites and trachytes, and related carbonatite-bearing terranes.’
- ‘In the Canaries, the lavas are much more compositionally varied in each of these stages, ranging from tholeiitic basalts to phonolites and trachytes.’
- ‘Sanidine is found only in quickly cooled lavas such as trachytes; microcline occurs in slowly cooled granites.’
- ‘The dominant magma types are basalts and hawaiites, with lesser amounts of trachytes, quartz trachytes, alkali rhyolites and phonolites.’
- ‘The mine workings occupy much of the west side of an isolated low hill composed mainly of light-colored volcanic rock, described as felsite porphyry or trachyte, highly altered to clay minerals.’
Early 19th century (denoting a volcanic rock with a rough or gritty surface): from Greek trakhus ‘rough’ or trakhutēs ‘roughness’.
We take a look at several popular, though confusing, punctuation marks.